Backyard Field Trips: Bringing Earth Science to Life on
Campus
Purpose: The purpose of this backyard field trip is to reinforce earth science concepts
using examples found on campus. One does not have to travel to the Grand Canyon or
Niagara Falls to reinforce many of the concepts discussed in class. This trip focuses on
weathering and fluvial features, rock types, and biogeography but can be adapted to suit
the interests and environment of the instructor.
Background: Central Michigan University, Mt. Pleasant, Michigan is located near the
center of Michigan's Lower Peninsula. Bedrock beneath campus is underlain by
Paleozoic sedimentary rocks buried by over 300 ft of glacial drift. Surface deposits
consist of beach deposits, ground moraine, and fluvioglacial deposits. Holocene Epoch
stream dissection is responsible for what little relief exists on campus. Soils are loamy
with numerous clay lenses. The original forest cover was beech maple with white pine,
ash, and basswood. Trees viewed on today's campus reflect native Michigan varieties as
well as exotic specimens. The average annual temperature is around 45 with winter
temperatures rarely falling below zero and
summer temperatures rarely piercing the 90
degree mark. Precipitation is distributed evenly
throughout the year. Snowfall averages around
35" annually, one of the lowest totals for the
entire state. The University was founded in 1892
but most of the buildings, sidewalks, and parking
lots were constructed in the 1950's and 1960's.
Our campus tour begins at Warriner Hall (pictured
to the left) which was constructed in the 1920's.
Stop 1: East Side of Warriner Hall--Part of stateliness of Warriner Hall is its ivy
covered walls. There is a price, however, for
using ivy as an ornamental. Observe the bricks
below the ivy with a hand lens. What do you
see? Write your answer in the space below.
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Biotic weathering takes two forms: chemical and physical. Ivy roots secrete acids to gain
a foothold in the brick. Acids are also secreted to dissolve nutrients from the brick.
Physical weathering occurs as roots wedge into brick cavities, prying loose pieces of
brick and cement. Unlike chemical weathering, this process does not chemically
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decompose the brick. Physical weathering does, however, aids the efficiency of chemical
weathering by increasing mineral and rock surface area.
Stop 2: Rock Garden North of Brooks Hall-Rocks boring? Never! Rocks are history
capsules with tales to tell on how they were
created. This stop features rocks from the three
rocks classes: sedimentary, metamorphic, and
igneous. The conglomerate is readily identified
by white pebbles encased by a tannish cement.
The well rounded to subrounded, as opposed to
angular, pebbles suggest erosion in a stream or
coastal environment before deposition and cementation.
Choose a quartzite tombstone. Why? This metamorphic rock is highly resistant to
weathering and erosion and will preserve an epitaph for millions of years. Note the cross
bedding present which suggests changing water or wind currents acting on the original
sand grains forming the rock. These sand grains eventually became cemented to form
sandstone. Plate collision or mountain building produced the intense heat and pressure
necessary to transform the sandstone to durable quartzite.
The rounded pillow structures on the basalt suggest a lava flow within an aqueous
environment. Quick cooling of the lava prevented the formation of crystals.
Stop 3: Differential Weathering on the
Heating Unit West of Brooks Hall--Compare
the north and west facing walls for brick
condition, color, and vegetation. Note that the
south facing wall has greater signs of
deterioration in terms of cracks, broken brick
faces, and general discoloration. Look on the
ground abutting the north facing wall. Moss is
present. How can these differences be
explained?
In the middle latitudes of the Northern
Hemisphere the sun is generally found in the
southern part of the sky. The south facing wall is more directly heated than the north or
east facing walls. What other evidence supports that the south side receives more direct
sunshine? Moss normally thrives where temperatures are cooler and soil conditions
moist. The north facing wall, away from direct sunlight, provides a more suitable habitat
for moss growth and propagation. At least two physical weathering processes are
operative at this stop. Minerals with bricks expand by different amounts creating stresses
within the cement and mortar. Repeated expansion and contraction cycles over the years
have weakened the cement holding brick together eventually causing rock and mineral
grains to mass waste from the wall.
Freeze-thaw action can also result in patterns of differential weathering. This type of
physical weathering is most active in December and March when temperatures hover
around the freezing point. First, sunlight thaws snow and ice; then water seeps into
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micro-fissures within bricks; finally, at night, water changes to ice. When water changes
to ice it occupies a volume of around 10% greater than the liquid state. Expansion during
this change in state widens fissures and breaks off pieces of brick.
Finally, observe the southwest corner of the building. This area is the most
weathered portion of the entire unit because brick corners are subject to weathering from
two sides. Temperatures are highest when the sun is in the southwestern part of the sky.
It is this southwest facing corner, therefore, that receives the greatest potential for
processes of freeze-thaw and thermal expansion. The west and south sides of these
corner bricks are weathered and are eventually "eaten through" creating the rounded
corners observed on this side. If corners weren't the first casualties of weathering square
rocks would be common.
Stop 4: Miniature Sinkholes North of Dow
Hall--The pitted surface, depressions, and caves
observable in this limestone boulder display, in
miniature, features associated with karst
terrains. The miniature sinkholes observed in
this picture could be created when joints were
solutionally enlarged by acidic rainwater.
Water combines with carbon dioxide to produce
carbonic acid which attacks calcium carbonate,
the main constituent of limestone. These
depressions could also be created when the
surface collapses due to the expansion of underlying caves. Humans have accelerated the
rates of limestone weathering through air pollution, specifically acid deposition. The
combustion of high sulfur coal from power plants releases sulfur oxides into the
atmosphere which then combine with water droplets to produce sulfuric acid. Acid
precipitation from human sources can lower the pH to 4.0 or lower, a thousand times
more acidic than neutral. Sulfuric acid can also coat dust particles which, when hydrated,
contribute to limestone solution.
Stop 5: Bald Cypress Tree (Taxodium Distichum) on the Southwest Side of Moore
Hall--On the annual academic pilgrimage to
Daytona Beach during spring break the
perceptive student may notice moss laden
conifers thriving in the swamps of Georgia
and Florida. This tree is a bald cypress, a
native of the deep South. What is this tree
doing almost a thousand miles outside of its
range? Observe characteristics of site: First,
note the heating duct in back of the tree.
Second, the tree faces south. Like the wall
observed during Stop 3, the south wall of a
building receives more direct solar heating. Third, this alcove protects the tree from cold
northwesterly winds. Collectively these site characteristics help explain how this
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southern species can survive snow and occasional sub-zero temperatures.
The bald cypress is an interesting tree. It's a deciduous conifer meaning that
although it is a needle-bearing tree needles are shed in the fall. The cypress is like a
maple tree in that it sheds its leaves (needles). The cypress is like a pine in that it has
needles instead of leaves. So much for the idea that all conifers keep their needles. As a
matter of fact, in any one year a conifer can lose up to one third of its needles as part of
the normal growth process. Another interesting trait of the bald cypress is that it often
grows bony stumps (knees) out of the water. These knees help support the tree which can
grow to heights of over one hundred feet and help roots obtain oxygen.
Stop 6: Root Wedging Northeast of the
Student Activity Center--This stop features
buckled pavement caused by the expansive
forces associated with root growth. Sidewalks
fractured by root growth will eventually have to
be replaced. Roots can also force their way
into sewage pipes causing tubs, sinks, and
toilets to backup.
While root growth can produce property
damage, roots have many valuable functions.
Roots retain soil helping to retard soil erosion. Roots breakup and help aerate soils,
aiding in plant growth. Finally, of course, if we had no roots we would have no food!
Stop 7: Delta Formed in Pond East of Student Activity Center--When vegetation is
cleared by forestry or construction soils are
often exposed to rainsplash and sheet erosion.
Soil particles become entrained in surface
runoff and are carried away by ephemeral
surface streams. A rapid reduction in stream
velocity occurs when streams or rivers empty
into a body of water. The transport capacity of
the stream is reduced causing sediments to fall
out of suspension and deposited in the form of a
delta.
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